REDISTRIBUTION OF ZINC FROM SEWAGE-SLUDGE APPLIED TO A RANGE OF CONTRASTING SOILS

An incubation study has been performed to investigate the rates of red istribution of Zn-65 from spiked sewage sludge into different soil fra ctions. The labeled zinc in soils amended with sludge was fractionated by operationally defined procedures at three different times (1, 7 an d 30 days after incubation) into exchangeable, organically bound, amor phous iron oxide-bound, crystalline iron oxide-bound and residual frac tions. The rates of redistribution of zinc from sewage sludge mainly d epended on soil pH. In acid soils, most of the sludge-derived zinc (70 -80%) went to the exchangeable pools, and was retained in this form at high concentration for at least a month. The effect of the time durin g digestion of the incorporation of a Zn-65 spike into sludge was also studied. Although the results were significantly effected by spike ti ming, the effects of the latter on subsequent zinc fractionation resul ts were minor compared with the effect of soil pH.